Northern Rivers RFS operations officer Daniel Ainsworth said morale was high among the troops, with several veterans of from previous major statewide firefighting deployments in 1994 and 2000 mixed in with newcomers.

"In the worst case we will be in purely property protection mode, but there are plans to put some defensive backburning in to try and lessen the impact on the towns," Mr Ainsworth said.

"That's when they basically stop fighting the fire and are simply protecting assets and the community."

Mr Ainsworth last visited Sydney in a major bushfire operation in 2003.

"But it's never been October - it doesn't usually start until summer," he said.

"Everyone's eager to help out, but I think it hasn't set in; the seriousness of how big the fire really is yet," he said.

"I think it will once we get to Sydney ... and they can actually see the smoke and see how big it is.

"The population is a lot denser to what we've got - it's basically urban interface firefighting."

Preparations are also in place to replace the crews come Thursday if required, with reinforcements flown down to allow the heavy equipment to stay thereremain in place.

Meanwhile, those who are stranded or cut off from their homes for more than 24 hours are not eligible for the latest round of federal disaster payments made available by the Coalition on Friday.

Federal Labor, who included that category of disaster victims in its payment scheme while in office, has attacked the move, labelling it "heartless".

Fire scientist says prospect for summer fire season "terrifying"

And a fire scientist has told the ABC's Lateline program he is worried about how the fire season will play out across Australia this year.

Fire scientist David Bowman from the University of Tasmania said the fire season tended to move from the north of Australia to the south across the summer and the fact these fires were happening so early in the season boded ill for the remainder of the season.

"It's terrifying," Prof Bowman told Lateline.

Prof Bowman said the only real hope of putting a stop to the bushfires running across NSW at the moment was a good "soaking" rain in the order of an ex-tropical cyclone.

"It's terribly worrying that we've got these fires starting this early in the season, because we've got to get through a summer yet.

"The reason I'm also very worried is that classically, the fire seasons move down from Queensland, NSW into Victoria and Tasmania.

"Our worst month in Tasmania is February and we saw a fire this year in January.

"Last summer was a reasonably benign fire season, and if you precondition it with a heatwave and very strong winds, you can switch what classically would just be a typical fire season, you can ramp it up as we saw in Dunalley, up into the catastrophic scale where again we were seeing fire behaviours which are just extraordinary."

Salvation Army Bushfire Appeal

Cash, not goods, needed most

Call 13 SALVOS (13 72 58)

Visit salvos.org.au

Or in person at any Westpac branch or Woolworths store

Woolworths matching public donations dollar for dollar for the next two weeks.